You have restated what I have come to understand is your position, but you have not addressed the following points: 1. pervect himself uses a "dropped mass" to measure the acceleration 2. pervect himself states that the dropped mass is just an instantaneously co-moving inertial observer 3. If spaceship B is always co-moving with the belt, (as you agreed), then their instantaneously co-moving inertial observers are identical at all times 4. Thus they would have to measure the same acceleration 5. Thus pervect's method does not support, and even contradicts, your claim that spaceship B and the belt would measure different accelerations 6. And pervect's method does support my claim that spaceship B and the belt would measure the same acceleration I do not have an account at that site, and am not interesting in making one. But if you do, and you would like to follow up with pervect, I would always welcome more information with an ever open mind. As I see it, you two disagree on that particular matter, with respect to post #50 in that thread. I understand the appeal of just having this end, due to the ongoing effort it requires. But that would be the easy way out, considering all of these unanswered questions.